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zfs: add idmapped mount support for rootless containers #621

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zfs: add idmapped mount support for rootless containers #621

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32 changes: 32 additions & 0 deletions storage/drivers/zfs/zfs.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import (
graphdriver "go.podman.io/storage/drivers"
"go.podman.io/storage/internal/tempdir"
"go.podman.io/storage/pkg/directory"
"go.podman.io/storage/pkg/idmap"
"go.podman.io/storage/pkg/idtools"
"go.podman.io/storage/pkg/mount"
"go.podman.io/storage/pkg/parsers"
Expand Down Expand Up @@ -470,6 +471,19 @@ func (d *Driver) Get(id string, options graphdriver.MountOpts) (_ string, retErr
}
}

// Apply idmapped mount if UID/GID mappings are explicitly provided
// This enables rootless container support by translating UIDs/GIDs
if len(options.UidMaps) > 0 || len(options.GidMaps) > 0 {
logrus.WithField("storage-driver", "zfs").Debugf("applying idmapped mount to %s with %d uid maps, %d gid maps", mountpoint, len(options.UidMaps), len(options.GidMaps))
if err := applyIDMappedMount(mountpoint, options.UidMaps, options.GidMaps); err != nil {
logrus.WithField("storage-driver", "zfs").Warnf("failed to apply idmapped mount to %s: %v", mountpoint, err)
if unmountErr := detachUnmount(mountpoint); unmountErr != nil {
logrus.WithField("storage-driver", "zfs").Warnf("failed to unmount %s after idmap failure: %v", mountpoint, unmountErr)
}
return "", fmt.Errorf("applying idmapped mount for zfs: %w", err)
}
}

return mountpoint, nil
}

Expand All @@ -494,6 +508,24 @@ func (d *Driver) Put(id string) error {
return nil
}

// applyIDMappedMount creates an idmapped mount over the ZFS mount to translate UIDs/GIDs
// for rootless container support. This uses the Linux mount_setattr() syscall with
// MOUNT_ATTR_IDMAP to create a view of the filesystem with translated ownership.
func applyIDMappedMount(mountpoint string, uidMaps, gidMaps []idtools.IDMap) error {
// Create a user namespace process with the desired UID/GID mappings
pid, cleanupFunc, err := idmap.CreateUsernsProcess(uidMaps, gidMaps)
if err != nil {
return fmt.Errorf("creating user namespace process for idmap: %w", err)
}
defer cleanupFunc()

// Apply the idmapped mount using the user namespace
if err := idmap.CreateIDMappedMount(mountpoint, mountpoint, pid); err != nil {
return fmt.Errorf("creating idmapped mount at %s: %w", mountpoint, err)
}
return nil
}

// ReadWriteDiskUsage returns the disk usage of the writable directory for the ID.
// For ZFS, it queries the full mount path for this ID.
func (d *Driver) ReadWriteDiskUsage(id string) (*directory.DiskUsage, error) {
Expand Down